This application claims the priority of application No. H10-156476, filed Jun. 4, 1998 in Japan, the subject matter of which is incorporated herein by reference.
The present invention relates to a board frame used for fabricating a semiconductor apparatus, using a transfer molding technique. The present invention also relates to a method for fabricating such a board frame.
A conventional semiconductor apparatus, which is fabricated using a BGA (Ball Grid Array) technique, includes a board frame, a semiconductor device (chip) and a mold package. Herein, the term xe2x80x9cboard framexe2x80x9d means a frame type of board or substrate that is used for fabricating semiconductor apparatuses. The board frame may employ a copper-plated-lamination structure. The semiconductor device is mounted on an island of the board frame. The semiconductor device is electrically connected at electrodes to inner leads provided on the board frame using a wire-bonding technique.
The board frame is provided at the bottom surface with solder balls. The inner leads are connected to outer leads using wires or through holes.
For a resin molding process, two major techniques, potting and transfer molding, are used. Transfer molding has been increasingly used, because semiconductor apparatuses can be easily fabricated with low costs, and mass production can be easily realized. The board frame can be provided as an individual piece, or as a frame, on which a number of semiconductor devices are mounted together. Frame types of boards (or substrates) have been increasingly employed for fabricating a transfer-mold type of semiconductor apparatuses.
In fabrication, the board frame with the semiconductor device is set between molding dies (die set). Then the molding resin is injected into the cavity at a predetermined pressure. As a result, the molding package is formed and the semiconductor device is sealed.
In recent years, as electric devices have been miniaturized, it has been required to miniaturize a package for semiconductor device as well. In order to miniaturize such a package, for example, the distance between the outer edge of the mold package and the outer edge of the board frame is shortened. However, the board frame must be mechanically held with the molding dies. Therefore, it is difficult to shorten such a distance.
In Japanese Patent Laying Open No. H9-252065, a wiring board region, which includes an island a semiconductor device is to be mounted on, is pushed off (removed) from a board frame, then the pushed off (removed) region is pushed back to the original position. After a transfer molding process, the wiring board region, which has been pushed back, is taken out from the board frame.
According to the conventional technology, shown in Japanese Patent Laying Open No. H9-252065, the wiring board region with the semiconductor device may have a difference in level from the remaining frame region. The level difference is caused by the push-back processing. The level difference may be in a range between 10 xcexcm and 20 xcexcm. According to the conventional method for push-back process, the wiring board region tends to be higher in level than the remaining frame region.
As it is difficult to control the level difference between the wiring board region and the remaining frame region, the yield rate of semiconductor apparatuses is lowered. When the level difference occurs between the wiring board region and the remaining frame region, it is difficult to carry out a wire bonding process properly and completely. Further, in a transfer molding process, thin burrs are made easily around the wiring board region.
As the wiring board region is pushed-back, the wiring region may drop out from the board frame. Especially when the gate is removed after the transfer molding process, the wiring board region easily drops out from the board frame. Consequently, according to the conventional technology, it is difficult to miniaturize a semiconductor apparatus without lowering the yield rate.
In this application, the term xe2x80x9cpush backxe2x80x9d means a process of removing a region once from the board frame, then soon returning it to the original position.
Accordingly, an object of the present invention is to provide a board frame with which a semiconductor apparatus can be fabricated easily to be small in size without lowering the yield rate.
Another object of the present invention is to provide a method for fabricating a board frame, with which a semiconductor apparatus can be fabricated easily to be small in size without lowering the yield rate.
A further object of the present invention is to provide a semiconductor apparatus that can be fabricated easily to be small in size without lowering the yield rate.
Additional objects, advantages and novel features of the present invention will be set forth in part in the description that follows, and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.
According to a first aspect of the present invention, a board frame includes a wiring board region, which includes an island on which a semiconductor device is to be mounted; and a marginal region surrounding the wiring board region. The board frame further includes a frame region, which is located around the marginal region; and a support region which connects the wiring board region and the frame region. The marginal region is removed from the board frame and is put back to its original position, while the wiring board region is maintained being connected to the frame region through the support region.
According to a second aspect of the present invention, a method for fabricating a board frame includes the step of providing on the board frame a wiring board region, which includes an island on which a semiconductor device is to be mounted. The method further includes the step of defining a marginal region which surrounds the wiring board region, a frame region that is located around the marginal region and a support region which extends between the wiring board region and the frame region through the marginal region so that the wiring board region and the frame region are connected to each other.
The method further includes the steps of removing the marginal region from the board frame and putting it back to its original position, while maintaining the wiring board region being connected to the frame region through the support region.
According to a third aspect of the present invention, a method for fabricating a semiconductor apparatus, which includes the step of providing on the board frame a wiring board region, which includes an island on which a semiconductor device is to be mounted. The method further includes the step of defining a marginal region which surrounds the wiring board region, a frame region that is located around the marginal region and a support region which extends between the wiring board region and the frame region through the marginal region so that the wiring board region and the frame region are connected to each other.
The method further includes the steps of removing the marginal region from the board frame and putting it back to its original position, while maintaining the wiring board region being connected to the frame region through the support region.
The method still further includes the steps of mounting the semiconductor device onto the island in the wiring board region; transfer-molding the semiconductor device using a die set, including a gate through which a thermosetting resin is guided in to a cavity thereof; and completely removing the marginal region from the board frame.
In each aspect of the present invention, preferably, the support region is shaped to have a width which is getting wider from the wiring board region toward the frame region.
As described above, according to the present invention, only the marginal region is pushed-back but the wiring board region is not pushed-back. The wiring board region is maintained being connected through the support region to the frame region. As a result, no level difference is made between the wiring board region and the frame region, and therefore, it is easy to carry out a wire bonding process properly and completely. Further, in a transfer molding process, thin burrs are not made easily around the wiring board region.
Further more, as the wiring board region is not pushed-back, the wiring board region does not drop out easily from the board frame. Consequently, semiconductor apparatuses can be fabricated easily to be small in size without lowering the yield rate.